self-complacency (n.)

word forming element indicating "oneself," also "automatic," from Old English use of self (pron.) in compounds, such as selfbana "suicide," selflice "self-love, pride, vanity, egotism," selfwill "free will." Middle English had self-witte "one's own knowledge and intelligence" (early 15c.).

OED counts 13 such compounds in Old English. Middle English Compendium lists four, counting the self-will group as a whole. It re-emerges as a living word-forming element mid-16c., "probably to a great extent by imitation or reminiscence of Greek compounds in (auto-)," and formed a great many words in the pamphlet disputes of the 17c.

"fact or state of being pleased with something or someone, especially oneself," 1640s, from same source as complacence but with the later form of the suffix (see -cy).

"pleased with oneself, self-satisfied," 1760, back-formation from self-complacency or else from self- + complacent. Related: Self-complacently.